| abstract |
Provided is a process which is intended to be employed in a refinery where decopperizing electrolysis slime and arsenic sulfide sediment are formed as intermediate products of nonferrous refining with the amount of the former being larger than that of the latter, and by which the disposal of arsenic is enabled without requiring that the mixing ratio between both intermediate products is kept at a specific level. Also provided is a process described above, wherein arsenic is converted into pentavalent arsenic in the leaching step, whereby the ratio of leaching of arsenic is enhanced. Specifically disclosed is a process which comprises: a leaching step of subjecting a mixed slurry of the intermediate products of nonferrous refining to oxidative leaching in an acid region to obtain a leach liquor; a liquor regulation step of adding an oxidizing agent to the leach liquor, thereby oxidizing arsenic into pentavalent arsenic, and thus obtaining a regulated liquor; and a crystallization step of converting the arsenic contained in the regulated liquor into scorodite crystals. The leaching step comprises: the first leaching step of adding elemental sulfur (S0) to the mixed slurry at the initiation of the reaction, and then leaching the slurry while adding an oxidizing agent thereto with the temperature raised to 50°C or above and with the pH adjusted to 1.0 to 2.0; the second leaching step of adjusting the pH to 2.0 or above by the addition of an alkali, and then leaching the slurry while adding an oxidizing agent thereto; and the third leaching step of stopping the addition of the oxidizing agent, and then further stirring the slurry. |